The present invention relates to accessories for use with marine outboard motors, and more particularly to a stabilizing device adapted to be mounted on a marine outboard motor to stabilize the engine against rocking, as well as decreasing torque steer and chine walk.
Marine outboard motors typically comprise a powerhead, a drive shaft housing attached to and suspended from the powerhead, a lower unit at the bottom end of the drive shaft housing, and a prop mounted at the lower unit. The outboard motor is mounted to the transom of a boat by a transom mounting bracket. The outboard motor is interconnected to the transom mounting bracket by an intervening tilt bracket which is connected to the transom mounting bracket and to the outboard motor. The tilt bracket is connected to the transom mounting bracket by a horizontal tilt pin which allows the outboard motor to be pivoted in a vertical plane into and out of the water. The tilt bracket is connected to the outboard motor by a vertical swivel pin which allows the outboard motor to be pivoted in a horizontal plane to steer the boat. The outboard motor is attached to the swivel pin by upper and lower motor swivel mounting brackets which are each attached at one end to the swivel pin and attached at the other end to th drive shaft housing. A steering arm is attached to the upper motor swivel mounting bracket and extends therefrom in a cantilever fashion over the top side boat transom. To steer the boat, the steering arm is moved in a horizontal plane to port or starboard thus causing the outboard motor to pivot about the vertical swivel pin in a horizontal plane changing the direction of the thrust vector generated by the prop. In order to dampen vibrations transmitted to the boat from the outboard motor to reduce vibration, noise, and structural fatigue to the boat, the outboard motor manufacturers use resilient motor mounts, usually rubber, at the connection of the upper and lower motor mounting bracket to the drive shaft housing.
Marine outboard motors are becoming more powerful each year. For example, factory stock motors of over 300 horsepower are now available. With these more powerful outboard motors the torque produced by the powerhead generates a substantial moment about the motor crankshaft and also about the center of the propeller which compresses the resilient motor mounts causing the outboard motor to "fish-tail". "Fishtailing" reduces the ability of the propeller to maintain a solid, continuous bite of the water. In addition, on V-bottom hull boats, the "fishtailing" of the engine will result in hull chine walk and on tunnel hulls it will result in the sponson-to-sponson bouncing. The compression of the resilient motor mounts also results in torque steering of the engine. These conditions decrease a driver's control over the boat.
An additional problem resulting from the compression of the resilient motor mounts is that the outboard motor, and more particularly the drive shaft housing, lower unit and propeller will crab or assume an angle to the direction of travel of the boat, i.e., in plan view the centerline of the propeller, and therefore the thrust vector generated by the propeller, will be at a slight angle to the longitudinal centerline or keel of the boat. A drive shaft housing and lower unit passing through water, at even a slight angle to the direction of travel, increases the possibility of propeller "blowout" or cavitation which causes the propeller to lose its bite. The result of propeller "blowout" can be a loss of control of the boat by the driver, damage to the propeller due to cavitation, and engine damage due to over-reving of the engine. In addition, the drive shaft housing and lower unit being at an angle to the direction of travel of the boat through the water is less hydrodynamic or streamlined than it is when in alignment with the direction of travel and, therefore, increases the hydrodynamic load or drag of the drive shaft housing and lower unit through the water.
U.S. Pat. No. 2,549,486 issued on Apr. 17, 1951 to E. C. Kiekhaefer shows a steering mounting for outboard motors. The function of the steering mounting device is to secure the outboard motor against a normal tendency of the motor to be turned on its steering axis by the vibration of the motor. The steering mounting device includes a circular bearing washer plate which has a central hole receiving the vertical pivot pin about which the outboard motor is pivoted to turn the boat to allow rotation of the washer plate relative to the vertical pivot pin. The washer plate also has flanges extending to each side of the vertical pivot pin. A compression spring is seated between each of these flanges and the outboard motor lower unit housing to secure the washer plate and outboard motor lower unit housing rotationally with respect to the axis of the pivot pin and to cushion the lower unit housing from vibration of the power unit. The entire weight of the power unit, and lower unit housing of the outboard motor are carried on the washer plate. The outboard motor is attached to the transom of a boat by a swivel bracket which is connected to the lower unit housing. A friction washer is located between the swivel bracket and bottom surface of the washer plate. A tiller handle is secured to the washer plate and extends over the swivel bracket into the boat. By securing the tiller handle to the washer plate, the handle is relieved or isolated from the vibration generated by the power unit. The device also includes adjustable pressure discs between the swivel bracket and washer plate bearing down against the upper surface of the washer plate. These adjustable pressure discs provide for the adjusting the frictional forces between the swivel bracket and washer plate to increase or decrease the steering effort of the motor about its steering axis to prevent the motor from turning by the vibration of the motor.
U.S. Pat. No. 2,714,362 issued on Aug. 2, 1955 to S. E. Schroeder teaches a steering adapter assembly for an outboard motor to adapt the outboard motor for steering from the forward portion of the boat to which the outboard motor is attached. The steering adapter assembly includes a bracket having two parallel rigid legs extending in one direction, and two parallel resilient arms extending in the opposite direction. The bracket is affixed to the outboard motor by bolts which attach the rigid legs to the outboard motor on opposite sides thereof so that the resilient arms extend to the rear of the outboard motor. A tiller rope is connected to the free ends of the resilient arms, and extend therefrom back over the boat transom to a steering wheel at the front of the boat. The resilient arms retain the tiller rope taut for effectively transmitting movement of the tiller rope to the motor for accurate steering control of the boat.
U.S. Pat. Nos. 2,549,496 and 2,714,362 are directed to devices for turning the outboard motor about a vertical pivot axis for pivoting the motor about this pivot axis to steer the boat to which the motor is attached. These steering devices do not address nor solve the above-discussed problems.
U.S. Pat. No. 3,613,631 issued on Oct. 19, 1971, to Gerald H. Wick shows a special transom mounting bracket secured to the engine about the power unit by an upper resilient mount and to the drive unit by a lower resilient mount to reduce the steering torque and vibration transmitted to the hand-held steering tiller of small engines. This proposed special mounting bracket does not solve the problems described above because it still relies on flexible mounts and is not suitable for high horsepower engines with remote steering systems. Furthermore, this special transom mounting bracket would be expensive because it would require a particularly designed motor and would not be practical as an after market replacement because it would involve extensive engine modifications.
A proposed solution to the above-discussed problems is to replace the resilient motor mounts with rigid mounts. This proposal may eliminate chine walk and torque steer due to compression of the flexible motor mounts, however, it is a difficult, time-consuming task to replace the mounts and, therefore, expensive. Furthermore, the substitution of rigid motor mounts for the flexible mounts will allow the engine vibration and engine forces to be transferred to the transom of the boat subjecting the transom to damage.